Patent GB-697549-A (GB)
Title: Improvements in electric signalling systems
IPC: B61L25/04
Filed: 1951-06-13
Abstract: 697,549. Electric selective signalling. GENERAL ELECTRIC CO., Ltd., and RALPH, F. E. April 25, 1952 [June 13, 1951], No. 13983/51. Class 40 (i). Two items of information represented by a number of impulses in impulse trains of different character are sent simultaneously over a single channel by interlacing the impulses, the last of the information conveying impulses of one signal being characterized by modification of the next impulse forming part of the other signal. The pulse trains may consist of positive and negative pulses respectively or of current pulses of two separate frequencies. As described, a train of 25 positive pulses interlaced with negative pulses is used, the destination and description of a train being represented by any number up to 25 of positive and negative pulses respectively. When the number of positive pulses transmitted corresponds to the destination, the next negative pulse is lengthened. Similarly, a lengthened positive pulse is sent when the number of negative pulses sent corresponds to the description. At the receiver, uniselectors are stepped respectively by the positive and negative pulses representing the information. Further uniselectors are stepped by the remaining positive and negative impulses, respectively, of the trains, at the end of which a total pulse count check is made before display or retransmission of the information. Transmission Fig. 1. Contacts of banks SA1, SB1 are marked corresponding to the " destination " and " description,"'respectively, and a transmit key closed to energize a start relay T, which locks, initiates the first (long) positive line impulse at contacts T5, T6, and energizes relays Y, TA, TB, followed by a slow-to-operate relay C. When C pulls up, it locks, releases Y, and operates a relay X, which in turn energizes the drive magnet SA of the " destination " uniselector SA1-SA4. A relay Z operated as Y releases operates the drive magnet SB of the " description " uniselector SB1-SB4, and de-energizes X. As X falls off it operates Y and releases the drive magnet SA to step the uniselector SA1. Relay Y operates a relay L to reverse the line current (first negative pulse), and releases Z, which re-operates X and releases the drive magnet SB to step the description uniselector SB1. Relay X re-operates drive magnet SA and releases Y to end the first negative impulse and commence the second positive impulse. As Y falls off it re-operates Z to re-operate drive magnet SB and releases X, which steps the uniselector SA1 and energizes Y. Relays X, Y, Z interact in this way to send short positive and negative impulses alternately over the line W1, W2, the destination and description uniselectors SA, SB being stepped at the end of each positive and negative impulse respectively. During this stepping, the slow-to-release relays TA, TB are held operated. When the destination selector SAl is stepped to its marked contact, relay Y operates to start the next negative line pulse, but relay Z is held over the destination marking for the falling off time of TA so that the negative pulse is lengthened. Thereafter, normal short pulses are sent as above described until 25 positive and 25 negative pulses have been sent, when the destination and description selectors stop on their normal contacts. Relay TB functions similarly to TA to hold relay X over the marked " description " contact in bank SB1 to lengthen the positive pulse following the last negative information pulse. A relay D operates when both TA, TB have relapsed, and when selectors SA1, SB1 have stepped to normal, TA, TB re-operate, and operate a relay ET, which de-energizes T. Reception, Fig. 2. The first (long) positive line pulse energizes the forward polarized line relay P to operate a slow-to-release relay RB, which in turn operates relays BA, CA, CB, AR, BR. When CA operates, the drive magnet A of a " destination " selector Al, A2 is energized by the line relay P and steps the selector when relay P relapses at the end of the positive pulse. Polarised line relay N is operated by the following negative pulse to energize the drive magnet B which, in a similar manner, steps the " description" selector B1, B2 and the negative pulse ends. The line relays P, N in this way advance the selectors A1-A2, B1-B2 in step with the corresponding " destination " and " description " selectors SA, SB at the transmitter in response to the short information pulses. When the lengthened negative pulse is sent the slow-torelease relay CA falls off so that all subsequent positive line pulses step a selector AC1, its drive magnet AC being energized in series with the upper wending of a relay AR, which falls when stepping ceases. Similarly, when the lengthened positive pulse is sent, relay CB falls so that subsequent negative pulses step a selector BC1 by way of drive magnet BC. Total pulse count check. The energization of relay ET at the transmitter, as above described, connects a relay RC across the iine wires W1, W2, in lieu of the supply. Provided all the receiver selectors have stepped correctly the relay RC is now energized in series with relay CC at the receiver over a circuit including banks A3, AC3, BC3, B3. Relay CC locks and operates the selected " destination and " description " indicator lamps over the banks A2, B2, the indication remaining until a " clear " key is thrown to release relay CC, when the receiver selectors step to normal ready to receive further signals. Relay RC reverts the transmitter to normal ready for further transmission. Should the total count check fail to operate relays RC, CC during release of relay T, a relay TF is operated, locks and lights an alarm lamp, which may be cleared, after eliminating the fault, by a reset key.